The nucleic acid hybridization method has been widely used in a variety of fields as a method having high specificity based on the complimentarity of nucleic acids.
The hybridization method includes, for example, dot hybridization wherein a nucleic acid is directly immobilized on a membrane, colony hybridization wherein a bacterium is incubated on a membrane, Southern blot technique wherein a nucleic acid is fractionated by electrophoresis as it is or upon cleavage with a restriction enzyme and transferred to a nitrocellulose membrane etc. for hybridization, and in site hybridization method done on a glass slide as described herein below.
An attempt has been made to immobilize a nucleic acid onto a microplate, beads, latex particles etc. rather than onto conventional membranes.
In addition, a DNA probe which is used for the above-exemplified hybridization varies depending on the marker (label) to be used including, for example, a probe reagent using a radioactive substance as a marker, a probe reagent using an enzyme as a marker, a probe reagent using a chemical fluorescent substance as a marker, a probe reagent using a chemical luminescent substance as a marker and so on.
Tests using a DNA probe for the diagnosis of infectious diseases and genetic disorders have been drawing much attention in recent years. In this connection, kits for diagnosis of infectious diseases using a DNA prove have been marketed.
In such a test, a step in the DNA probe assay particularly requires handling of a trace amount of a sample with precision for a long time tedious and time-consuming work to do. What is more, the assay is susceptible to an error due to inconsistent control of hybridization temperatures by an individual operator and contamination due to a very low concentration of a sample. Motivated thereby, there is a great demand in the market for a system enabling an automated mechanical assay of a DNA probe, which is still left to be satisfied.
Accordingly, an object of the present invention is to provide an apparatus for an automated assay suitable for a DNA probe hybridization method, comprising measurement of an optically-measurable change in a substrate, which is caused by catalysis of an enzyme used as a marker.
Another object of the present invention is to provide a device for measuring light, which comprises a simple light-shielding structure permitting effective shielding of light from outside during measurement of the target light, and an apparatus for an automated assay comprising this light measurement device.
Still another object of the present invention is to provide a device for measuring light with high measurement precision, which permits prevention of outside light and stray light from invading into a light receiving part of an emitted light detection part when a light measurement is or is not underway, and an apparatus for an automated assay comprising this light measurement device.
A further object of the present invention is to provide a method for assaying a nucleic acid in a sample, which permits efficient and continuous measurement of a multitude of samples.